Autonomic neuropathy is a debilitating complication of diabetes mellitus. Once autonomic dysfunction is established the disorder is progressive and affects multiple organ systems. Current therapies for this syndrome are frequently unsatisfactory, and fail to arrest or reverse the underlying disease process. We suspect that therapeutic intervention in diabetic autonomic neuropathy, in order to be successful, must be instituted at an early stage in this disorder. Currently there is no way of predicting autonomic dysfunction in diabetic patients prior to the onset of symptoms. Although autonomic reflex tests have made it possible to diagnose autonomic involvement early in the natural history of diabetes, there is no evidence that asymptomatic patients who perform poorly on autonomic function tests are likely to develop clinical symptoms of autonomic neuropathy. For this reason we are interested in developing other methods for diagnosing early autonomic involvement in diabetes. Our hypothesis is that incipient diabetic autonomic neuropathy can be predicted in patients who show evidence of decreased norepinephrine production.